The invention relates generally to computer networks, and deals more particularly with a network server that permits a network client to access a local resource coupled directly to the network server and a remote resource coupled to a host computer.
A previously known local area network (LAN) is used to interconnect multiple personal computers or work stations, called "clients", and a network server. The network server comprises a personal computer and a program which provides a variety of services to the clients. For example, the server manages a local disk (DASD) and permits selected (or all) clients on the LAN to access the disk. Also, the server may provide access by LAN clients to a local printer that the server manages. To access the local disk, the client must first establish a session or "log-on" to the server with a valid account and password and request a connection to the local disk. In response, the server validates the account and password, and grants the connection if available. Then, the client requests a remote file operation (e.g. open, read, write, close) and furnishes associated parameters. In response, the server may copy (depending on the operation) the file from the local disk into RAM, and performs the operation requested by the client. If the file is updated, the server will copy the updated version back to the local disk, overwriting the previous version.
A previously known IBM LANRES/VM computer system comprises a LAN, a network server and a remote disk driver (with a remote disk) coupled to the network server. The remote disk driver is in the form of a System/370 host computer; however, the System/370 computer is not used as a computer for service to the network server, but merely as a disk driver for the remote disk. The network server maintains a list of all resources that the network server can access, i.e. the local disk, the remote disk, all directories on the local disk and all directories on the remote disk, and a table or pointers to map each directory and file within the directory to the storage location on the corresponding disk. The clients do not know where the requested resource resides. To access any of the resources, a client on the LAN must establish a session with or log-on to the network server with a valid account and password, request a connection to a named resource and provide a remote file operation/command and associated parameters. In response, the network server validates the account and password, determines the location of the named resource and then translates the directory name into specific addresses on the disk. If the file is located on the local disk, then the network server fetches the directory from the addresses and then performs the operation requested by the client. (The client may subsequently request access to a file within the directory.) If the file is located on the remote disk, then the server provides to the remote disk driver the specific addresses of the directory on the remote disk to be written to or read from and the write or read command. It should be noted that the network server cannot address the remote disk by a directory (or file) name, and the disk driver does not provide the security associated with a log-on requirement. Also, because the data cannot be accessed by a directory (or file) name or as any discernible entity, it is not possible for another application program which executes on the System/370 computer to access the directory or file; this other application program does not know the location of the directory or file. Nevertheless, there is an important advantage to this LANRES/VM computer system. As noted above, the client need not know the actual location of the disk; the disk can be local to the network server or connected to the remote disk driver. In this respect, the server is "transparent" to the client.
A general object of the present invention is to provide a network server which permits a client on a network to access a local resource managed by the network server and a remote resource managed by a host computer, which host computer provides host computer services relating to the remote resource.
Another object of the present invention is to provide a network server of the foregoing type which permits a client to access both a local resource and a remote resource without knowing the location of either.
Still another object of the present invention is to provide a network server of the foregoing type which permits an application program executing on the host computer to access the same directories and files on the remote resource that the clients can access.
A more specific object of the present invention is to provide a network server of the foregoing type in which the host computer provides security for the remote resource.
Another specific object of the present invention is to provide a network server of the foregoing type which permits a client to access remote resources managed by different host computers, and to do so efficiently.